CN112670577A - Electrolyte, preparation method thereof and lithium ion battery - Google Patents

Electrolyte, preparation method thereof and lithium ion battery Download PDF

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CN112670577A
CN112670577A CN202011539960.7A CN202011539960A CN112670577A CN 112670577 A CN112670577 A CN 112670577A CN 202011539960 A CN202011539960 A CN 202011539960A CN 112670577 A CN112670577 A CN 112670577A
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additive
electrolyte
carbonate
lithium
organic solvent
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CN112670577B (en
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邹志群
曾汉民
何巍
袁中直
刘建华
刘金成
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Eve Energy Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0567—Liquid materials characterised by the additives
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells

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Abstract

The invention provides an electrolyte, a preparation method thereof and a lithium ion battery. The electrolyte comprises additives, wherein the additives comprise an unsaturated carbonate additive, a lithium salt additive, an additive A and an additive B, and the additive B comprises an isocyanuric acid derivative. The preparation method comprises the following steps: and mixing the additives with other raw materials according to the formula amount under a protective atmosphere to obtain the electrolyte, wherein the additives comprise an unsaturated carbonate additive, a lithium salt additive, an additive A and an additive B. The electrolyte provided by the invention solves the problem that the cycle performance, the high-temperature performance, the normal-temperature performance and the low-temperature power performance of the battery electrolyte are difficult to be considered at the same time.

Description

Electrolyte, preparation method thereof and lithium ion battery
Technical Field
The invention belongs to the technical field of batteries, and relates to an electrolyte, a preparation method thereof and a lithium ion battery.
Background
In recent years, high-nickel materials are applied to batteries of electric vehicles, but the increase of the Ni content originally improvesThe less safe thermal stability of the ternary material becomes less controllable. The NCM and the LMFP are compounded, so that the safety of the battery can be effectively improved, but the LMFP has the problems of low electronic conductivity and ion diffusion and being influenced by Jahn-Taller, the material has poor circulation performance, and Mn is dissolved out to aggravate material attenuation especially under the high-temperature condition. The high nickel ternary is easy to generate cation mixed discharge due to the increase of the content of the Ni element, and simultaneously, the high nickel ternary is easier to mix with water and CO under the condition of high temperature2The reaction causes the gas production of the battery to affect the cycle. And power battery group is in-service use, even if there is the management and control of BMS, the module temperature rise also often reaches more than 40 ℃, consequently how to promote cycle life and the high temperature storage of battery under the high temperature condition and become very important problem, can also have performances such as power concurrently simultaneously.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide an electrolyte, a preparation method thereof and a lithium ion battery.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides an electrolyte comprising additives including an unsaturated carbonate additive, a lithium salt additive, an additive a and an additive B, the additive B comprising an isocyanuric acid derivative.
In the electrolyte provided by the invention, various additives which are matched with each other solve the problem that the circulation performance, the high-temperature performance and the power performance of the electrolyte are difficult to be considered at the same time.
Specifically, in the electrolyte system provided by the invention, the unsaturated carbonate additive has the advantages that a film is formed on a negative electrode; the lithium salt additive has the effect of forming a film by a positive electrode and a negative electrode, can enable the generated SEI film to be compact, can inhibit metal ions of the positive electrode from dissolving out, weakens the damage of the metal ions to the SEI film of the negative electrode, and improves the thermal stability of the formed film; the additive A can play a role in auxiliary film formation of a negative electrode in an electrolyte system, and meanwhile, the film formation impedance is low and the thermal stability is good; the additive B can play a role in stabilizing the electrolyte and forming a film on the positive electrode in an electrolyte system, and the formed SEI film has a role in stabilizing the boron-containing coating layer of the positive electrode.
In summary, the invention effectively improves the problems of instability of the surface film of the anode/cathode, severe gas expansion of the battery in high-temperature storage and poor high-temperature cycle performance by means of the synergistic effect of the additives in a mode of simultaneously adding the unsaturated carbonate additive, the lithium salt additive, the additive A and the additive B;
meanwhile, the additive can be added into the quick-charging electrolyte besides the common electrolyte, so that the performance can be maintained, the good quick-charging cycle performance and power performance of the quick-charging electrolyte can be maintained, and the performance of the quick-charging cycle and the like of the quick-charging electrolyte can not be reduced after the traditional additive is added.
Preferably, in the electrolyte provided by the invention, the isocyanuric acid derivative has a general structural formula
Figure BDA0002854617730000021
Wherein X comprises methyl, ethyl, n-propyl, allyl, chlorine or fluorine;
preferably, the isocyanuric acid derivative comprises any one or a combination of at least two of trimethyl isocyanurate, triethyl isocyanurate, tripropyl isocyanurate, triallyl isocyanurate, trichloroisocyanuric acid and trifluoroisocyanuric acid, and the specific structural formula is as follows:
Figure BDA0002854617730000022
the following is a preferred technical solution of the present invention, but not a limitation to the technical solution provided by the present invention, and the technical objects and advantageous effects of the present invention can be better achieved and achieved by the following preferred technical solution.
In a preferred embodiment of the present invention, the unsaturated carbonate additive comprises any one or a combination of at least two of vinylene carbonate VC, fluoroethylene carbonate FEC, or vinylene carbonate VEC.
Preferably, the lithium salt additive comprises lithium bis (fluorosulfonyl) imide LiFSI, lithium difluorophosphate LiPO2F2Any one or a combination of at least two of lithium bis (oxalato) borate LiBOB, lithium bis (oxalato) borate LiODFB, lithium difluoro (oxalato) phosphate LiODFP, and lithium tetrafluoro (oxalato) phosphate LiTFOP.
Preferably, the additive a is a sulfopropionic anhydride derivative.
Preferably, the general structural formula of the additive A is
Figure BDA0002854617730000031
Wherein R is1、R2、R3、R4Hydrogen, methyl or form a benzene ring with sulfonic anhydride;
preferably, the sulfopropionic anhydride derivative comprises any one of 2-sulfopropionic anhydride, 3, 4-dimethyl-2-sulfopropionic anhydride, 4-dimethyl-2-sulfopropionic anhydride or 2-sulfobenzoic anhydride or a combination of at least two thereof.
The specific structural formula is as follows:
Figure BDA0002854617730000032
preferably, the mass fraction of the unsaturated carbonate additive in the electrolyte is 0.2-1.0%, such as 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1.0%. In the present invention, if the amount of the unsaturated carbonate additive is too small, a dense SEI film cannot be formed; if the amount of the unsaturated carbonate added is too large, the resistance becomes large and high-temperature gassing occurs.
Preferably, the mass fraction of the lithium salt additive in the electrolyte is 0.5-2.0%, such as 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2.0%, etc. In the present invention, if the lithium salt additive is too little, a dense SEI film cannot be formed, and good power performance cannot be ensured; if the lithium salt additive is too much, gas generation may occur.
Preferably, the mass fraction of the additive a in the electrolyte is 0.2-1.0%, such as 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1.0%. In the present invention, if the additive a is too small, it may result in failure to form a dense SEI film on the negative electrode; if additive A is too much, excessive film formation, rapid charge cycle and power performance degradation may result.
Preferably, the mass fraction of additive B in the electrolyte is 0.1-1.0%, such as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1.0%, etc. In the invention, if the additive B is too little, an effective SEI film cannot be formed on the positive electrode, and the high-temperature improvement is not obvious; if too much additive B is present, it will lead to increased impedance, rapid charge cycles and reduced power performance.
As a preferable technical solution of the present invention, the electrolyte further includes an organic solvent and an electrolyte salt. In the present invention, the electrolyte salt is different from the lithium salt additive.
Preferably, the electrolyte is an electrolyte of a high nickel battery. The electrolyte provided by the invention is particularly suitable for high-nickel batteries.
In a preferred embodiment of the present invention, the organic solvent includes a cyclic carbonate and a chain carbonate.
Preferably, the cyclic carbonate includes ethylene carbonate and/or propylene carbonate.
Preferably, the chain carbonate includes any one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate or propyl methyl carbonate or a combination of at least two thereof.
If the requirements on quick charging and power are high, dimethyl carbonate can be added; if the requirement on the quick charging system is not high or no requirement, other chain carbonates except dimethyl carbonate can be added.
Preferably, the organic solvent can also comprise chain carboxylic ester, and the coordination of the chain carboxylic ester and the organic solvent ensures that the electrolyte has higher conductivity and lower viscosity, improves the rate capability of the electrolyte, and is beneficial to improving the quick charging performance.
Preferably, the chain carboxylate comprises any one of methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate or butyl butyrate or a combination of at least two thereof.
Preferably, the volume fraction of the cyclic carbonate in the organic solvent is 20 to 40%, for example 20%, 25%, 30%, 35%, 40% or the like, the volume fraction of the dimethyl carbonate is 0 to 20%, for example 0%, 10%, 12%, 14%, 16%, 18%, 20% or the like, the volume fraction of the chain carbonate other than the dimethyl carbonate in the chain carbonate is 40 to 70%, for example 40%, 45%, 50%, 55%, 60%, 65%, 70% or the like, and the volume fraction of the chain carboxylate in the chain carbonate is 0 to 20%, for example 0%, 5%, 10%, 15%, 18%, 20% or the like.
Preferably, the organic solvent is composed of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate and chain carboxylic acid esters.
Preferably, in the organic solvent, the volume fraction of ethylene carbonate is 20-40%, such as 20%, 25%, 30%, 35%, 40% or the like, the volume fraction of dimethyl carbonate is 10-20%, such as 10%, 12%, 14%, 16%, 18%, 20% or the like, the volume fraction of ethyl methyl carbonate is 40-70%, such as 40%, 45%, 50%, 55%, 60%, 65%, 70% or the like, the volume fraction of chain carboxylic ester is 10-20%, such as 10%, 12%, 14%, 15%, 16%, 18%, 20% or the like
In the electrolyte provided by the invention, the organic solvent can account for 80-85% of the mass fraction of the whole electrolyte system.
In a preferred embodiment of the present invention, the electrolyte salt includes lithium hexafluorophosphate LiPF6Lithium hexafluoroarsenate LiAsF6Lithium perchlorate LiClO4At least one of lithium bis (fluorosulfonyl) imide LiFSI, lithium tetrafluoroborate LiBF4, and lithium bis (trifluoromethanesulfonyl) imide LiTFSI.
Preferably, the electrolyte salt has a concentration of 1.0 to 1.5mol/L, such as 1.0mol/L, 1.1mol/L, 1.2mol/L, 1.3mol/L, 1.4mol/L, or 1.5mol/L, etc., in the electrolyte solution.
In a second aspect, the present invention provides a method for preparing the electrolyte according to the first aspect, the method comprising the steps of:
and mixing the additives with other raw materials according to the formula amount under a protective atmosphere to obtain the electrolyte, wherein the additives comprise an unsaturated carbonate additive, a lithium salt additive, an additive A and an additive B.
The preparation method provided by the invention is simple to operate and short in flow, and can meet the requirement of industrial large-scale production.
In a preferred embodiment of the present invention, the other raw materials include an organic solvent and an electrolyte salt in a formula amount.
Preferably, the mixed raw materials are added in the order of adding the additive to the organic solvent and then adding the electrolyte salt.
Preferably, the mixing is stirred mixing.
Preferably, the temperature of the mixing is 5-20 ℃, such as 5 ℃, 6 ℃, 7 ℃, 8 ℃, 9 ℃ or 10 ℃ and the like. The aim of adopting lower mixing temperature is to prevent the free acid of the electrolyte from rising caused by the thermal decomposition of lithium salt and additives.
Preferably, the protective atmosphere comprises a nitrogen atmosphere and/or an argon atmosphere.
As a preferred technical scheme of the invention, the preparation method comprises the following steps:
under protective atmosphere, adding unsaturated carbonate additive, lithium salt additive, additive A and additive B in formula amounts into an organic solvent, then adding electrolyte salt, stirring and mixing to obtain the electrolyte.
In a third aspect, the present invention provides a lithium ion battery comprising the electrolyte according to the first aspect.
As a preferable technical solution of the present invention, the lithium ion battery further includes a positive electrode, a negative electrode, and a separator.
Preferably, the active material of the positive electrode is a high nickel ternary material. The high-nickel ternary material is characterized in that the molar percentage of nickel element in three metal elements except lithium in the ternary material is more than 50%.
Preferably, the active material of the positive electrode includes a nickel cobalt manganese ternary material and/or a nickel cobalt aluminum ternary material.
In the invention, the chemical formula of the nickel-cobalt-manganese ternary material can be represented as follows: li (Ni)xCoyMnz)O2Wherein 0.5<x≤0.8，0<y≤0.2，0<z is less than or equal to 0.3 and x + y + z is 1.
Preferably, the chemical formula of the nickel-cobalt-aluminum ternary material is as follows: li (Ni)xCoyAlz)O2Wherein 0.5<x≤0.8，0<y≤0.2，0<z is less than or equal to 0.05 and x + y + z is 1.
Preferably, the active material of the negative electrode includes graphite.
Compared with the prior art, the invention has the following beneficial effects:
(1) in the electrolyte system provided by the invention, the unsaturated carbonate additive is used as a negative electrode film-forming additive, and can play a role in forming a compact SEI film on the surface of a graphite negative electrode in the electrolyte system, so that the structural stability of a negative electrode material is improved, the circulating impedance of a battery is reduced, and the circulating performance of the battery is improved; the lithium salt additive has the functions of enhancing the stability of the positive and negative electrode surface films at high temperature, improving the high-temperature storage performance and inhibiting the gas production in the battery in an electrolyte system; in an electrolyte system, the additive A forms a compact SEI film with good lithium conducting performance on a negative electrode, so that the high-temperature performance and the power performance are improved; the additive B has an amide structure, so that electrolyte salt can be stabilized in an electrolyte system, and a positive electrode film formed by oxidizing the anode with cyclic amide has a complexing effect with certain coating layers (such as boron-containing coating layers) of the anode, so that the stability of the anode coating layer is effectively improved, the high-temperature performance of the electrolyte is favorably improved, and the high-temperature storage gas generation of the battery is reduced.
(2) The preparation method provided by the invention is simple to operate and short in flow, and can meet the requirement of industrial large-scale production.
Detailed Description
In order to better illustrate the present invention and facilitate the understanding of the technical solutions of the present invention, the present invention is further described in detail below. The following examples are merely illustrative of the present invention and do not represent or limit the scope of the claims, which are defined by the claims.
The following are typical but non-limiting examples of the invention:
example 1
The present embodiment provides an electrolyte composed of an organic solvent, an electrolyte salt, and an additive. The additive is unsaturated carbonate additive, lithium salt additive, additive A and additive B.
The unsaturated carbonate additive is vinylene carbonate, and the mass fraction of the unsaturated carbonate additive in the electrolyte is 0.8%;
the lithium salt additive is bis-fluorosulfonyl imide lithium, and the mass fraction of the lithium salt additive in the electrolyte is 2%;
the additive A is 2-sulfobenzoic anhydride (compound 10) with the mass fraction of 0.6 percent in the electrolyte;
the additive B is trimethyl isocyanurate (compound 1), and the mass fraction of the additive B in the electrolyte is 0.6%.
The lithium salt is lithium hexafluorophosphate, and the concentration of the lithium salt in the electrolyte is 1.0 mol/L.
The organic solvent consists of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate and chain carboxylic ester (ethyl propionate), wherein the volume fraction of the ethylene carbonate is 30%, the volume fraction of the dimethyl carbonate is 15%, the volume fraction of the ethyl methyl carbonate is 40% and the volume fraction of the chain carboxylic ester is 15% based on 100% of the total volume of the organic solvent; the organic solvent accounts for 83.5 percent of the electrolyte by mass percent, calculated by taking the electrolyte mass percent as 100 percent.
The embodiment also provides a preparation method of the electrolyte, which comprises the following specific steps:
adding unsaturated carbonate additive, lithium salt additive, additive A and additive B in formula amounts into an organic solvent under argon atmosphere, then adding electrolyte salt, and stirring and mixing at 15 ℃ to obtain the electrolyte.
The test results of the electrolyte prepared in this example are shown in table 1.
Example 2
The present embodiment provides an electrolyte composed of an organic solvent, an electrolyte salt, and an additive. The additive is unsaturated carbonate additive, lithium salt additive, additive A and additive B.
The unsaturated carbonate additive is fluoroethylene carbonate, and the mass fraction of the unsaturated carbonate additive in the electrolyte is 0.6 percent;
the lithium salt additive is lithium difluorophosphate, and the mass fraction of the lithium salt additive in the electrolyte is 1.0%;
the additive A is 2-sulfopropionic anhydride (compound 7), and the mass fraction of the additive A in the electrolyte is 0.8%;
the additive B is triethyl isocyanurate (compound 2), and the mass fraction of the additive B in the electrolyte is 0.4%.
The lithium salt is lithium hexafluorophosphate, and the concentration of the lithium salt in the electrolyte is 1.2 mol/L.
The organic solvent consists of ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate and chain carboxylic ester (methyl propionate), wherein the volume fraction of the ethylene carbonate is 20%, the volume fraction of the dimethyl carbonate is 10%, the volume fraction of the methyl ethyl carbonate is 60% and the volume fraction of the chain carboxylic ester is 10% based on 100% of the total volume of the organic solvent. (ii) a The organic solvent accounts for 82.2 percent of the electrolyte by mass percent, calculated by taking the electrolyte mass percent as 100 percent.
The embodiment also provides a preparation method of the electrolyte, which comprises the following specific steps:
adding unsaturated carbonate additive, lithium salt additive, additive A and additive B in formula amounts into an organic solvent under argon atmosphere, then adding electrolyte salt, and stirring and mixing at the temperature of 5 ℃ to obtain the electrolyte.
The test results of the electrolyte prepared in this example are shown in table 1.
Example 3
The present embodiment provides an electrolyte composed of an organic solvent, an electrolyte salt, and an additive. The additive is unsaturated carbonate additive, lithium salt additive, additive A and additive B.
The unsaturated carbonate additive is a mixture of vinylene carbonate and fluoroethylene carbonate (the mass ratio of the vinylene carbonate to the fluoroethylene carbonate is 1:1), and the mass fraction of the unsaturated carbonate additive in the electrolyte is 1.0 percent;
the lithium salt additive is lithium bis (oxalato) borate, and the mass fraction of the lithium salt additive in the electrolyte is 0.5%;
the additive A is 4, 4-dimethyl-2-sulfopropionic anhydride (compound 8) with the mass fraction of 1.0 percent in the electrolyte;
the additive B is trichloroisocyanuric acid (compound 5), and the mass fraction of the additive B in the electrolyte is 1.0%.
The lithium salt is lithium hexafluorophosphate, and the concentration of the lithium salt in the electrolyte is 1.2 mol/L.
The organic solvent consists of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate and chain carboxylic ester (propyl acetate), wherein the volume fraction of the ethylene carbonate is 30%, the volume fraction of the dimethyl carbonate is 10%, the volume fraction of the ethyl methyl carbonate is 50% and the volume fraction of the chain carboxylic ester is 10% based on 100% of the total volume of the organic solvent. The organic solvent accounts for 81.5 percent of the electrolyte by mass percent, calculated by taking the electrolyte mass percent as 100 percent.
The embodiment also provides a preparation method of the electrolyte, which comprises the following specific steps:
adding unsaturated carbonate additive, lithium salt additive, additive A and additive B in formula amounts into an organic solvent under argon atmosphere, then adding electrolyte salt, and stirring and mixing at 15 ℃ to obtain the electrolyte.
The test results of the electrolyte prepared in this example are shown in table 1.
Example 4
The present embodiment provides an electrolyte composed of an organic solvent, an electrolyte salt, and an additive. The additive is unsaturated carbonate additive, lithium salt additive, additive A and additive B.
The unsaturated carbonate additive is a mixture of vinylene carbonate and fluoroethylene carbonate (the mass ratio of the vinylene carbonate to the fluoroethylene carbonate is 1:3), and the mass fraction of the unsaturated carbonate additive in the electrolyte is 1.0 percent;
the lithium salt additive is lithium difluorobis (oxalato) phosphate, and the mass fraction of the lithium salt additive in the electrolyte is 1.0%;
the additive A is 3, 4-dimethyl sulfopropionic anhydride (compound 9) with the mass fraction of 0.2 percent in the electrolyte;
and the mass fraction of the additive B, namely triallylisocyanurate (compound 4) in the electrolyte is 0.1 percent.
The lithium salt is lithium hexafluorophosphate, and the concentration of the lithium salt in the electrolyte is 1.2 mol/L.
The organic solvent consists of ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate and chain carboxylic ester (methyl butyrate), wherein the volume fraction of the ethylene carbonate is 20%, the volume fraction of the dimethyl carbonate is 20%, the volume fraction of the methyl ethyl carbonate is 40% and the volume fraction of the chain carboxylic ester is 20% based on 100% of the total volume of the organic solvent. The organic solvent accounts for 82.7 percent of the electrolyte by mass percent, calculated by taking the electrolyte mass percent as 100 percent.
The test results of the electrolyte prepared in this example are shown in table 1.
Example 5
The present embodiment provides an electrolyte composed of an organic solvent, an electrolyte salt, and an additive. The additive is unsaturated carbonate additive, lithium salt additive, additive A and additive B.
The unsaturated carbonate additive is vinylene carbonate, and the mass fraction of the unsaturated carbonate additive in the electrolyte is 0.8%;
the lithium salt additive is bis-fluorosulfonyl imide lithium, and the mass fraction of the lithium salt additive in the electrolyte is 2%;
the additive A is 2-sulfobenzoic anhydride (compound 10) with the mass fraction of 0.6 percent in the electrolyte;
the additive B is trimethyl isocyanurate (compound 1), and the mass fraction of the additive B in the electrolyte is 0.6%.
The lithium salt is lithium hexafluorophosphate, and the concentration of the lithium salt in the electrolyte is 1.0 mol/L.
The organic solvent consists of ethylene carbonate and methyl ethyl carbonate, wherein the volume fraction of the ethylene carbonate is 30% and the volume fraction of the methyl ethyl carbonate is 70% based on 100% of the total volume of the organic solvent; the organic solvent accounts for 83.5 percent of the electrolyte by mass percent, calculated by taking the electrolyte mass percent as 100 percent.
The embodiment also provides a preparation method of the electrolyte, which comprises the following specific steps:
adding unsaturated carbonate additive, lithium salt additive, additive A and additive B in formula amounts into an organic solvent under argon atmosphere, then adding electrolyte salt, and stirring and mixing at 15 ℃ to obtain the electrolyte.
The test results of the electrolyte prepared in this example are shown in table 1.
Comparative example 1
The electrolyte provided by this comparative example was the same as the electrolyte of example 1 in all respects except that the additive contained no unsaturated carbonate additive.
The test results of the electrolyte prepared in this comparative example are shown in table 1.
Comparative example 2
The electrolyte provided in this comparative example was the same as the electrolyte of example 1 in all respects except that the additive contained no lithium salt additive.
The test results of the electrolyte prepared in this comparative example are shown in table 1.
Comparative example 3
The electrolyte provided by this comparative example was the same as the electrolyte of example 1 in all respects except that the additive contained no additive a.
The test results of the electrolyte prepared in this comparative example are shown in table 1.
Comparative example 4
The electrolyte provided by this comparative example was the same as the electrolyte of example 1 in all respects except that the additive contained no additive B.
The test results of the electrolyte prepared in this comparative example are shown in table 1.
Comparative example 5
The electrolyte provided by this comparative example was the same as the electrolyte of example 5 in all respects except that the additive contained no additive a.
The test results of the electrolyte prepared in this comparative example are shown in table 1.
Comparative example 6
The electrolyte provided by this comparative example was the same as the electrolyte of example 5 in all respects except that the additive contained no additive B.
The test results of the electrolyte prepared in this comparative example are shown in table 1.
Test method
The electrolytes provided in the examples and comparative examples were applied to lithium ion batteries, and performance tests were performed using the lithium ion batteries. The specific preparation method of the lithium ion battery for testing comprises the following steps: preparing a negative electrode material graphite, a conductive agent acetylene black and a binder SBR into slurry according to the mass percentage of 94:1:5, coating the slurry on a copper foil current collector, and drying in vacuum to obtain a negative electrode plate; preparing a positive electrode material NCM811, a conductive agent acetylene black and a binder PVDF into slurry according to a mass ratio of 94:3:3, coating the slurry on an aluminum foil current collector, and drying in vacuum to obtain a positive electrode plate. And assembling the positive pole piece, the negative pole piece, the Celgard2400 diaphragm and the electrolyte prepared in the embodiment or the comparative example into a soft package battery, and performing electrochemical test by adopting a Xinwei charge-discharge test cabinet.
(1) And (3) testing the cycle performance of the lithium ion battery:
charging the lithium ion battery to a voltage of 4.2V at a constant current of 1.5C (nominal capacity) at a temperature of 25 ℃/45 ℃, then charging to a current of less than or equal to 0.05V at a constant voltage of 4.2V, standing for 10min, and discharging to a cut-off voltage of 2.8V at a constant current of 1C, wherein the above is a charge-discharge cycle. Carrying out 1500 times of charge-discharge cycles on the lithium ion battery at 25 ℃ according to the conditions; 1000 charge-discharge cycles at 45 ℃.
The capacity retention (%) after N cycles of the lithium ion battery was ═ x 100% (discharge capacity at the N-th cycle/first discharge capacity), and N was the number of cycles of the lithium ion battery.
(2) Testing the power performance of the lithium ion battery:
at 25 ℃, the lithium ion battery is charged to a voltage of 4.2V at a constant current of 1C, then charged to a current of 0.05C at a constant voltage of 4.2V, and then discharged for 30min at a constant current of 1C, namely the state of charge of the lithium ion battery is 50% SOC. And then discharging for 30s at 25 ℃ in a 2C pulse mode and discharging for 10s at-20 ℃ in a 0.33C pulse mode, and measuring the direct current impedance (DCR) of the lithium ion battery to represent the normal-temperature power performance and the low-temperature power performance of the lithium ion battery.
DCR ═ voltage before discharge-voltage at end of pulse discharge)/(discharge current).
(3) Testing the high-temperature storage performance of the lithium ion battery:
charging the lithium ion battery to 4.2V at a constant current of 1C at 25 ℃, then charging to 0.05C at a constant voltage of 4.2V, and testing the volume of the lithium ion battery to be V0; and then putting the lithium ion battery into a constant temperature box with the temperature of 60 ℃, storing for 30 days and 60 days respectively, taking out the lithium ion battery, and testing the volume of the lithium ion battery and recording as Vn.
The lithium ion battery has a volume expansion ratio (%) of (Vn-V0)/V0 × 100% after n days of storage at 60 ℃.
The test results are shown in the following table:
TABLE 1
Figure BDA0002854617730000141
It can be known from the above examples and comparative examples that the electrolyte provided by the examples is added with an unsaturated carbonate additive as a negative electrode film-forming additive to form a dense SEI film on the surface of a graphite negative electrode, thereby improving the structural stability of the negative electrode material, reducing the cycle impedance of the battery, and improving the cycle performance of the battery; by adding lithium salt additives into the electrolyte, the stability of the positive and negative electrode surface films at high temperature is enhanced, the high-temperature storage performance is improved, and the gas production rate in the battery is inhibited; an SEI film with compact and good lithium conducting performance is formed on a negative electrode by adding the additive A into the electrolyte, so that the high-temperature and power characteristics are improved; by adding the additive B into the electrolyte, the electrolyte salt can be stabilized due to the amide structure, and the anode film formed by oxidizing the anode with the cyclic amide has a complexing effect with certain coating layers (such as boron-containing coating layers) of the anode, so that the stability of the anode coating layer is effectively improved, the high-temperature performance of the electrolyte is favorably improved, and the high-temperature storage gas generation of the battery is reduced.
Comparative example 1 resulted in a decrease in cycle performance because it did not contain the unsaturated carbonate additive.
Comparative example 2 does not contain a lithium salt additive, resulting in a decrease in cycle performance and low temperature power performance.
Comparative examples 3 and 5, which contain no additive A, have poor high-temperature cycle performance and high-temperature storage performance.
Comparative examples 4 and 6 contain no additive B, and therefore, the high-temperature cycle performance and the high-temperature storage performance are significantly deteriorated.
Comparison between examples 1-4 and comparative examples 3 and 4 shows that the addition of the additive A, B in the rapid-charging solvent system significantly improves the high-temperature cycle and high-temperature storage of the battery, the normal-temperature cycle does not significantly decrease, and the normal-temperature DCR and the low-temperature DCR do not significantly improve, which proves that the addition of the additive A, B can improve the high-temperature performance of the battery on the basis of maintaining the original cycle performance and power performance of the battery. The problem that the fast charging cycle performance, the high-temperature performance, the normal-temperature performance and the low-temperature power performance of the electrolyte of the high-nickel battery are difficult to be considered is solved.
Comparison of example 5 with comparative examples 5 and 6 shows that the addition of the additive A, B in the non-fast-charging solvent system can improve the high-temperature performance of the battery on the basis of maintaining the original cycle performance and power performance of the battery.
The applicant states that the present invention is illustrated in detail by the above examples, but the present invention is not limited to the above detailed methods, i.e. it is not meant that the present invention must rely on the above detailed methods for its implementation. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.

Claims (10)

1. An electrolyte comprising additives, wherein the additives comprise an unsaturated carbonate additive, a lithium salt additive, an additive a, and an additive B, wherein the additive B comprises an isocyanuric acid derivative.
2. The electrolyte of claim 1, wherein the isocyanuric acid derivative has a general structural formula
Figure FDA0002854617720000011
Wherein X comprises methyl, ethyl, n-propyl, allyl, chlorine or fluorine;
preferably, the isocyanuric acid derivative comprises any one of or a combination of at least two of trimethyl isocyanurate, triethyl isocyanurate, tripropyl isocyanurate, triallyl isocyanurate, trifluoroisocyanuric acid, and trichloroisocyanuric acid;
preferably, the unsaturated carbonate additive comprises any one of Vinylene Carbonate (VC), fluoroethylene carbonate (FEC) or Vinyl Ethylene Carbonate (VEC) or a combination of at least two of the Vinylene Carbonate (VC), the fluoroethylene carbonate (FEC) or the Vinyl Ethylene Carbonate (VEC);
preferably, the lithium salt additive comprises lithium bis (fluorosulfonyl) imide LiFSI, lithium difluorophosphate LiPO2F2Any one or a combination of at least two of lithium bis (oxalato) borate LiBOB, lithium bis (oxalato) borate LiODFB, lithium bis (oxalato) phosphate LiODFP or lithium tetrafluorooxalato phosphate LiTFOP;
preferably, the additive a is a sulfopropionic anhydride derivative;
preferably, the sulfopropionic anhydride derivative comprises any one of 2-sulfopropionic anhydride, 3, 4-dimethyl-2-sulfopropionic anhydride, 4-dimethyl-2-sulfopropionic anhydride or 2-sulfobenzoic anhydride or a combination of at least two thereof;
preferably, in the electrolyte, the mass fraction of the unsaturated carbonate additive is 0.2-1.0%;
preferably, in the electrolyte, the mass fraction of the lithium salt additive is 0.5-2.0%;
preferably, in the electrolyte, the mass fraction of the additive A is 0.2-1.0%;
preferably, in the electrolyte, the mass fraction of the additive B is 0.1-1.0%.
3. The electrolyte of claim 1 or 2, further comprising an organic solvent and an electrolyte salt;
preferably, the electrolyte is an electrolyte of a high nickel battery.
4. The electrolyte of claim 3, wherein the organic solvent comprises a cyclic carbonate and a chain carbonate;
preferably, the cyclic carbonate includes ethylene carbonate and/or propylene carbonate;
preferably, the chain carbonate comprises any one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate or propyl methyl carbonate or a combination of at least two of the above;
preferably, the organic solvent further includes chain carboxylic ester;
preferably, the chain carboxylic acid ester comprises any one of methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate or butyl butyrate or a combination of at least two of them;
preferably, in the organic solvent, the volume fraction of the cyclic carbonate is 20-40%, the volume fraction of the dimethyl carbonate is 0-20%, the volume fraction of chain carbonates except the dimethyl carbonate is 40-70%, and the volume fraction of the chain carboxylate is 0-20%;
preferably, the organic solvent consists of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate and chain carboxylic ester;
preferably, in the organic solvent, the volume fraction of the ethylene carbonate is 20-40%, the volume fraction of the dimethyl carbonate is 10-20%, the volume fraction of the methyl ethyl carbonate is 40-70%, and the volume fraction of the chain carboxylic ester is 10-20%.
5. The electrolyte of any one of claims 1-4, wherein the electrolyte salt comprises lithium hexafluorophosphate LiPF6Lithium hexafluoroarsenate LiAsF6Lithium perchlorate LiClO4Lithium bis (fluorosulfonyl) imide LiFSI and lithium tetrafluoroborate LiBF4And lithium bistrifluoromethanesulfonylimide, LiTFSI;
preferably, the concentration of the electrolyte salt in the electrolyte is 1.0-1.5 mol/L.
6. A method of preparing the electrolyte of any of claims 1-5, comprising the steps of:
and mixing the additives with other raw materials according to the formula amount under a protective atmosphere to obtain the electrolyte, wherein the additives comprise an unsaturated carbonate additive, a lithium salt additive, an additive A and an additive B.
7. The method of claim 6, wherein the other raw materials include organic solvents and electrolyte salts in formulated amounts;
preferably, the mixed raw materials are added in the order of adding the additive into the organic solvent and then adding the electrolyte salt;
preferably, the mixing is stirring mixing;
preferably, the temperature of the mixing is 5-20 ℃;
preferably, the protective atmosphere comprises a nitrogen atmosphere and/or an argon atmosphere.
8. The method for preparing according to claim 6 or 7, characterized in that it comprises the following steps:
under protective atmosphere, adding unsaturated carbonate additive, lithium salt additive, additive A and additive B in formula amounts into an organic solvent, then adding electrolyte salt, stirring and mixing to obtain the electrolyte.
9. A lithium ion battery comprising the electrolyte of any one of claims 1 to 5.
10. The lithium ion battery of claim 9, further comprising a positive electrode, a negative electrode, and a separator;
preferably, the active material of the positive electrode is a high nickel ternary material;
preferably, the high-nickel ternary material is a ternary material which contains more than 50% of nickel element in mole percentage in other three metal elements except lithium;
preferably, the active material of the positive electrode comprises a nickel-cobalt-manganese ternary material and/or a nickel-cobalt-aluminum ternary material;
preferably, the chemical formula of the nickel-cobalt-manganese ternary material is as follows: li (Ni)xCoyMnz)O2Wherein 0.5<x≤0.8，0<y≤0.2，0<z is less than or equal to 0.3 and x + y + z is 1;
preferably, the chemical formula of the nickel-cobalt-aluminum ternary material is as follows: li (Ni)xCoyAlz)O2Wherein 0.5<x≤0.8，0<y≤0.2，0<z is less than or equal to 0.05 and x + y + z is 1;
preferably, the active material of the negative electrode includes graphite.
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